Fluoropolymers, i.e. polymers having a fluorinated backbone, have been long known and have been used in a variety of applications because of several desirable properties such as heat resistance, chemical resistance, weatherability, UV-stability etc. The various fluoropolymers are for example described in “Modern Fluoropolymers”, edited by John Scheirs, Wiley Science 1997. Commonly known or commercially employed fluoropolymers include polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) (FEP polymers), perfluoroalkoxy copolymers (PFA), ethylene-tetrafluoroethylene (ETFE) copolymers, terpolymers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride (VDF) (so called THV copolymers) and polyvinylidene fluoride polymers (PVDF). Commercially employed fluoropolymers also include fluoroelastomers and thermoplastic fluoropolymers.
Several methods are known to produce fluoropolymers. Such methods include suspension polymerization, aqueous emulsion polymerization, solution polymerization, polymerization using supercritical CO2, and polymerization in the gas phase. In the polymerization of fluoromonomers, traditionally the monomers are added to a kettle along with an initiator, to initiate the polymerization, as well as a solvent, and in the case of aqueous emulsion polymerization, the polymerization is carried out in water and typically in the presence of a surfactant, in order to stabilize the emulsion.
Aqueous emulsion polymerization normally involves the polymerization in the presence of a fluorinated surfactant, which is generally used for the stabilization of the polymer particles formed. Suspension polymerization generally does not involve the use of surfactant but results in substantially larger polymer particles than in case of the aqueous emulsion polymerization. Thus, the polymer particles in case of suspension polymerization will quickly settle out whereas in case of dispersions obtained in emulsion polymerization generally good stability over a long period of time is obtained. It is generally recognized that an aqueous emulsion polymerization where no surfactant is used to generally produce homo- and copolymers of chlorotrifluoroethylene (CTFE).
Notwithstanding the fact that emulsifier free polymerizations are known, the aqueous emulsion polymerization process in the presence of surfactants is still a desirable process to produce fluoropolymers because it can yield stable fluoropolymer particle dispersions in high yield. Emulsion polymerization processes have been carried out using various fluorinated surfactants, such as, for example, perfluoroalkanoic acid or salt thereof as a surfactant. Perfluoroalkanoic acid or salt thereof were the preferred surfactants because they provided a wide variety of desirable properties such as high speed of polymerization, good copolymerization properties of fluorinated olefins with comonomers, small particle sizes of the resulting dispersion can be achieved, good polymerization yields i.e. a high amount of solids can be produced, good dispersion stability, etc. Due to environmental concerns, however, perfluoroalkanoic acid or salt thereof was recently replaced with other fluorinated surfactants, such as, for example linear and branched partially or perfluorinated polyethers. In order to achieve product characteristics similar to those achieved when using perfluoroalkanoic acid or salt thereof, however, the aforementioned fluorinated emulsifiers must be used in higher quantities than perfluoroalkanoic acid or salt thereof and generally require the addition of an inert perfluorochemical during aqueous emulsion polymerization of the fluoromonomers.
There is needed a more effective surfactant that can increase polymerization rates and be effective at even lower levels, which would save production costs, such as, for example on surfactant recovery systems. There is also a need for a surfactant that does not require addition of an inert fluorochemical during aqueous emulsion polymerization of the fluoromonomers. There is also a need for a surfactant that become part of the resulting fluoropolymer, which would eliminate the need for surfactant recovery and recycle equipment and processes.